1. Field of the invention
This invention relates to resin compositions being excellent in transparency and gas barrier property, as well as in flexibility as represented by resistance to dropping shock, flexural resistance, ability to prevent air-back, skin-pack adaptability, shrink-packaging capability, and the like; and further to multilayer structures comprising at least one layer of the composition.
2. Description of the Prior art
Saponified products of ethylene-vinyl acetate copolymers (hereinafter referred to as EVOH) are thermoplastic resins excellent in transparency, gas barrier property, resistance to oil and odor-keeping property as compared to other resins, and are thereby used for various gas-barrier films and for gas-barrier layers of various gas-barrier containers. However, multilayered films and multilayered containers comprising an EVOH as barrier layer often generate problems resulting from the high rigidity of EVOH. For example, a multilayered film or container filled with contents readily breaks when dropped onto the floor, a multilayered film filled with contents tends to generate thereon pinholes by action of bending and/or shock when transported, a multilayered tube often generates air-back, wrinkle generation upon skin-pack packaging, insufficient stretchability and/or shrinkage of films for shrink-packaging and so forth.
Blending other thermoplastic resins with EVOH has been tried to overcome the above-mentioned drawbacks. Thus, for example, Japanese Patent Application Laid-Open No. 220839/1986 discloses that blending EVOH with an ethylene-carboxylic acid vinyl ester copolymer or ethylene-acrylic acid ester copolymer improves the flexural resistance; and Japanese Patent Application Laid-Open No. 81448/1986 (U.S. Pat. No. 4,645,695) discloses that blending EVOH with an ethylene-carboxylic acid vinyl ester copolymer or ethylene-acrylic acid ester copolymer modified with an .alpha.,.beta.-unsaturated carboxylic acid or its anhydride improves the shock resistance of EVOH. While these methods improve flexural resistance and impact strength of EVOH, they impair the transparency characteristic to EVOH, thereby being inapplicable to such uses as require transparency.
Compositions comprising EVOH and polyamide are known to have high transparency. However, since blending of a polyamide results in a decrease in gas barrier property and worsens thermal stability at molding, thereby causing generation of gels in a short period of molding, such blended compositions have not been put to practical use.
Japanese Patent Publication No. 48512/1976 and japanese Patent Application Laid-Open Nos. 73984/1977, 77160/1977, 101182/1977, 53089/1979, 156082/1979 and 161447/1985 disclose about blending with EVOH a partially saponified product of ethylene-vinyl acetate copolymer (hereinafter referred to as "partially saponified EVA"), and that the use of such blend will give interfacial adhesiveness between EVOH and polyolefin or heat sealability at low temperatures.
Actual preparation of molded articles such as film according to the process described in the above-mentioned prior arts has, however, encountered such problems as insufficient flexibility and poor thermal stability of obtained molded articles, poor surface appearance of obtained films such as streaks and pear skinned pattern and poor moldability due to frequent neck-in; and the process has thereby not been put into practical use yet. Nothing is thus known about the fact that a transparent gas-barrier resin composition can be obtained by blending EVOH with a partially saponified EVA both having specific melt indexes and vinyl alcohol component contents at a specific blending ratio, according to the present invention.
There have yet been thus obtained no transparent resin compositions or multilayered structures thereof having improved the flexibility of EVOH as represented by resistance to dropping shock, flexural resistance, prevention of air-back, skin-pack adapatability, shrink-packaging capability.